The present invention relates to an indwelling catheter, more specifically to an indwelling catheter to be left in the blood vessel to perform infusion, introduction of a medical solution, blood transfusion, blood collection, monitor of blood circulation, etc.
An indwelling needle for infusion, transfusion, etc. has a plastic catheter tube capable of being left in place in the blood vessel with a distal end communicated with a tube extending from a receptacle, such as a infusion bag, containing a fluid, medicinal solution, blood, etc. A type of the indwelling needle has an integral structure through which a sharp-tipped internal needle made of metals, etc. extends. This type of the indwelling needle is inserted into the blood vessel together with the internal needle, which is then withdrawn from the catheter to conduct infusion, transfusion, etc. in the same manner as above.
Since the lumen of the catheter inserted into the body must be maintained large enough to effectuate the infusion and introduction of a medicinal solution, which are primary objectives of the indwelling needle, the catheter is required to have a high kink resistance. Further, the catheter is required to have sufficient stiffness for the insertion into the blood vessel and to soften after being left in the blood vessel, etc., because the mechanical properties of the catheter largely affect the puncture of the skin, the insertion of the catheter into the blood vessel and the indwelling of the catheter.
The conventional indwelling catheters are mainly made of fluoroplastics such as polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymers, etc. Although the catheters made of fluoroplastics are sufficiently stiff for penetrating the skin and for insertion into the blood vessel, they do not sufficiently soften in contact with the blood. Therefore, the indwelling catheters made of fluoroplastics are likely to damage the inner wall of the blood vessel. Also, they are insufficient in kink resistance, posing the problems that they collapse in the blood vessel, preventing smooth flow of the infusion fluid.
In view of such circumstances, polyurethane resins having soft segments of polytetramethylene glycols have recently become widely used for the indwelling catheters. Japanese Patent Publication (JPB) 8-11129 discloses a catheter tube softening in the blood vessel, which is made of a hydrophilic polyetherurethane, the catheter tube having controlled balance between stiffness at the time of insertion and softness after being left in the blood vessel. However, the indwelling catheters made of polyetherurethanes are disadvantageous in failing to exhibit a sufficient kink resistance even after insertion into the blood vessel, although they become soft in contact with the blood. When the catheters are made stiffer for ease of insertion, their kink resistance is further deteriorated.
The catheters made of polyurethane resins can be improved in change in Young""s modulus and in kink resistance by controlling molecular weights of the soft segments of the polyurethane resins. However, when only a polyurethane resin comprising a soft segment constituted by a polyglycol having a molecular weight of 500-1500 is used, the resultant catheter has insufficient kink resistance or never recovers its original shape once kinked even if the kink resistance is sufficient, though it exhibits large change in Young""s modulus when changed from a dry condition at 25xc2x0 C. to a wet condition at 37xc2x0 C. On the other hand, when only a polyurethane resin comprising a soft segment constituted by a polyglycol having a molecular weight of 1500-3000 is used, the resultant catheter fails to exhibit large change in Young""s modulus when changed from a dry condition at 25xc2x0 C. to a wet condition at 37xc2x0 C., though its kink resistance is sufficient. Thus, polyurethane resins having soft segments of substantially a single molecular weight fail to satisfy both requirements of change in Young""s modulus and kink resistance.
Japanese Patent 2,723,190 discloses an indwelling needle made of shape-memory resins. A catheter of this indwelling needle exhibits sufficient stiffness at the time of insertion into the blood vessel and becomes soft after being left in the blood vessel. However, because such change of stiffness occurs too rapidly, it may become soft during the operation of insertion, making the insertion operation difficult.
An object of the present invention is, therefore, to provide an indwelling catheter exhibiting as high stiffness as the fluoroplastic catheters at the time of insertion into the blood vessel and becoming soft after being left in the blood vessel, while exhibiting modulus decrease behavior suitable for indwelling operations and sufficient kink resistance.
As a result of research in view of the above object, the inventors have paid attention to the fact that it is important to control the speed of decrease in Young""s modulus when changed from a dry condition at 25xc2x0 C. to a wet condition at 37xc2x0 C. in order that the indwelling catheter exhibits good stiffness (operability) at the time of insertion and becomes soft after inserted into the blood vessel, thereby avoiding the blood vessel from being damaged, that when the speed of decrease in Young""s modulus is too slow, it takes too much time until the indwelling catheter becomes soft, thereby being likely to cause damage to the blood vessel after indwelled, and that when the Young""s modulus of the indwelling catheter decreases too rapidly, the indwelling catheter becomes soft during the operation of insertion, thereby making the operation difficult.
What has been found as a result of investigation of the softening behavior of the polyurethane resins based on such findings is generally that how the polyurethane resins soften mostly depends upon the crystallinity of polyglycols contained in the polyurethane resins. When low-molecular weight polyglycols are contained in the polyurethane resins, the polyurethane resins are less likely to have large crystallinity, thus being accelerated in crystalline melting. As a result, the polyurethane resins exhibit an increased softening speed as temperature rises.
Because polymers having similar molecular structures generally have good compatibility, an additivity rule may be applicable to their blends. Accordingly, it may be expected that if a plurality of polyurethane resins having soft segments with different molecular weights were blended, or if a polyurethane resin were composed of a hard segment and a soft segment which is formed from a plurality of polyglycols having different molecular weights, their averaged properties would be obtained. However, the inventors have found that the additivity rule does not apply to the properties of such polyurethane resins as materials for the indwelling catheters. As a result of research, the inventors have found that when an indwelling catheter is made of a blend produced by combining a plurality of polyurethane resins each having poor properties, or when an indwelling catheter is made of a polyurethane resin produced by combining a plurality of polyglycols each forming a polyurethane resin with poor properties, the resultant indwelling catheter not only exhibits substantially the same stiffness as the fluoroplastic catheters at the time of insertion into the blood vessel and becomes soft after being left in the blood vessel, thereby avoiding the blood vessel from being damaged and showing decrease in Young""s modulus suitable for the operation of indwelling, but also has excellent kink resistance. The present invention is based on this finding.
Thus, the indwelling catheter according to the present invention has a dynamic storage modulus of 1 GPa or more under a dry condition at 25xc2x0 C. and showing decrease in dynamic storage modulus when changed from a dry condition at 25xc2x0 C. to a wet condition at 37xc2x0 C., a decrease percentage Ep of the dynamic storage modulus, which is represented by the following equation:
Ep=[(E0xe2x88x92Et)/(E0xe2x88x92E30)]xc3x97100%,
wherein E0 is a dynamic storage modulus under the dry condition at 25xc2x0 C., E30 is a dynamic storage modulus at the elapsed time of 30 minutes after placed under the wet condition at 37xc2x0 C., and Et is a dynamic storage modulus at the elapsed time of t after placed under the wet condition at 37xc2x0 C., being less than 60% at the elapsed time of 20 seconds after placed under the wet condition at 37xc2x0 C. and 60% or more at the elapsed time of 1 minute after placed under the wet condition at 37xc2x0 C.
The first example of the indwelling catheter exhibiting such decrease percentage of dynamic storage modulus is formed from a blend of a plurality of polyurethane resins containing polyglycols having different molecular weights. Each polyurethane resin preferably comprises a diisocyanate, a diol chain extender and polyglycols, the polyglycols having different molecular weights. A plurality of polyurethane resins preferably comprise a first polyurethane resin containing 20-70 weight % of polyglycol having a molecular weight of 500-1500 and a second polyurethane resin containing 20-70 weight % of polyglycol having a molecular weight of 1500-3000, the difference in molecular weight between the polyglycol in the first polyurethane resin and the polyglycol in the second polyurethane resin being 500 or more. Each of the polyurethane resins is preferably a reaction product of 4,4xe2x80x2-diphenylmethane diisocyanate, 1,4-butanediol and polycaprolactone glycol and has a Shore hardness of 60 D or more.
The second example of the indwelling catheter exhibiting a similar decrease percentage of dynamic storage modulus is made of a polyurethane resin containing a plurality of polyglycols having different molecular weights. The polyglycols contained in the polyurethane resin may be the same as described above, and other components constituting the polyurethane resin may also be the same as described above. The polyurethane resin preferably has a Shore hardness of 60 D or more.
The indwelling catheter according to a preferred embodiment of the present invention has a kink resistance of 10 mm or more both under a dry condition at 25xc2x0 C. and a wet condition at 37xc2x0 C. It also has a Young""s modulus of 50 kgf/mm2 or more under a dry condition at 25xc2x0 C., which reduces to 25 kgf/mm2 or less within 5 minutes when placed under a wet condition at 37xc2x0 C.